optimum height of burst

For nuclear weapons and for a particular target (or area), the height at which it is estimated a weapon of a specified energy yield will produce a certain desired effect over the maximum possible area.

Operation Tumbler-Snapper — Photograph taken milliseconds after detonation of nuclear device from the Snapper phase of the Tumbler Snapper test series. (The shot tower is faintly visible below fireball). Information Country United States Test site … Wikipedia